PURPOSE: To promptly perform 2/4-cycle switching by simple constitution by providing a liftable sleeve valve in an intake port for a 2-cycle engine, and utilizing a pressure of air, sucked by controlling an intake control valve and a pressure valve, to move the sleeve valve.

CONSTITUTION: In the case of use as a 2-cycle engine, an intake control valve 7, provided in an intake passage 6, is opened, on the other hand to close a pressure valve 10 provided in a branch pipe 9. Thus by applying a boost pressure of supercharge air from a turbocharger compressor 8 to act, a sleeve valve 5, provided in an intake port 2, is lifted to open the intake port 2. In the case of use as a 4-cycle engine, the intake control valve 7 is closed, on the other hand to open the pressure valve 10. Thus by lowering down the sleeve valve 5 by the boost pressure of supercharge air, the intake port 2 is closed. Here in a control unit 18, a control signal in accordance with an input detection signal of each sensor 19 to 21 is output to each actuator 11, 12.